CA1051589A - Phase boundary process for the preparation of aromatic polycarbonates using a chlorinated aromatic hydrocarbon as the polymer solvent - Google Patents

Abstract

A PHASE BOUNDARY PROCESS FOR THE PREPARATION
OF AROMATIC POLYCARBONATES USING A CHLORINATED
AROMATIC HYDROCARBON AS THE POLYMER SOLVENT

Abstract of the Invention The present invention provides a process for the preparation of a polycarbonate by the phase boundary conden-sation method, by phosgenation of an aqueous alkali metal salt solution of one or more aromatic dihydroxy compounds, in which process an aromatic chlorinated hydrocarbon is used as the solvent and the synthesis of the polycarbonate is carried out in two stages, in the first stage of which the reaction of the alkali metal salt solution of the aromatic dihydroxy compound(s) with phosgene is carried out at an OH concentration of between 0.01 and 0.1% by weight of OH, relative to the aqueous phase, in the presence of 0.1 to 2.5 mol% of trialkyl-amine, relative to aromatic dihydroxy compound(s), and at a temperature higher than 70°C, with a dwell time of less than 5 minutes, while in the second stage the polycondensation is effected by adjusting the OH concentration to 0.20 to 0.50%
by weight of OH, relative to the aqueous phase, optionally with further addition of trialkylamine, at a temperature higher than 80°C and with a dwell time of more than 1 minute.
.

Description

Mo-1486~P
LeA 15,514 ~5~

A PHASE BOUNDARY PROCESS FOR THE PREPARATION
OF AROMATIC POLYCARBONATES USING A CHLORINATED
~ROMATIC HYDROCARBON AS THE POLYMER SOLVENT

Back~round of the Invention ~-A current commercial process for the preparation of aromatic polycarbonates is ~he phase boundary condensation process. According to this process an aqueous bis-phenolate - -solution is reacted in phosgene with a suitable solvent for the polycarbonate, optionally in the presence of chain stoppers and with further addition of aqueous alkali metal ~ ;
hydroxide solu~ion.

Solvents recommended for this process are preferably -~
chlorinated hydrocarbons such as, for example, methylene chloride, chloroform, 1,2-dichloroe~hane and chlorobenzene.
While, the use of methylene chloride or 1,2-dichloroethane alone or mixed with other solvents, including, for example, chIorobenzene, presents no special problems, the use of chloro- ~ ;~
benzene alone entails great difficulties. These difficulties ~`
result from the extremely low solubility o the polycarbonates in chlorobenzene at tempera~ures below 80C. Thus, for example, 10% strength polycarbonate solutions (bisphenol A
type) in chlorobenzene are stable only at temperatures in excess of about 30C and 20% strength solutions are only ;~
stable at above about 70C. At the customary reaction temp-eratures of ~5-30C, only about 8 g of polycarbonate will dissolve in 100 g of chlorobenzene. ~ `

Therefore, if it is desired to use chlorobenzene as the sole solvent in the synthesis of polycarbonate by t.he phase boundary process, it is necessary to maintain reaction temperatures of or in excess of 70C.

LeA 15,514 ~ .

1~5151~9 The use of chlorobenzene is of great interest for various reasons including the follo~ing: ~

1. better chemical stability, in comparison to , the aliphatic chlorina~ed hydrocarbons, towards the alkaline reaction solution, and very good heat stability when isolating the polycarbonates in evaporation extruders at temperatures between 300 and 350C, so that light colored poly-carbonates are obtained; ~ -~

2. a simpler and more reliable form of recovery `
from the process effluents, due to the sub-stantially lower solubility and volatility of chlorobenzene resulting in impro~ed ecological and economical performance and;

- 3. less corrosion when recovering the solvent by distillation in the presence of water.

Though the reasons mentioned suggest the industrial use of chlorobenzene in the preparation of polycarbonates, industrial use ha~ hitherto been prevented by the difficulties which oacur during phosgenation at elevated temperatures. It becomes difficult to reproducibly conduct the condensation reaction. Saponification reactions occur with both the phos-gene and the oligomeric intermediate products having chloro-carbonic acid ester end groups. The reaction requires ~;

increased amounts of phosgene compared to lower temperaturephosgenation and it becomes impossible to control the molecular weight distribution of the finished polymer to the degree of precision desired. It is believed that this is because at an .~ ;
elevated reaction temperature the saponification reaction of phosgene or of the chlorocarbonic acid ester groups is greatly favored compared to the propagation reaction which leads to LeA 15,514 -2- -, - ~

S~S89 ~`~
the formation of the carbonate polymer. A consequence is that `;
the bisphenols employed are not incorporated quantitatively ~ -into the product. ~;

It is clear that an increased consumption of phosgene, .
incomplete incorporation of the bisphenols employed and ; -molecular weights which do not have the desired values for the ;-~ --particular grade of product, thus producing waste material -are severe economic and technical disadvantages. ~ ~-Summary of the_Invention The subject of the present invention is a process for the preparation of high molecular, aromatic polycarbonates by the phase boundary condensation method, by phosgenation of an aqueous alkali metal salt solution of aromatic dihydroxy compounds, characterized in that aromatic chlorinated hydro-carbons are uqed as the sole polycarbonate solvents and in that the synthesis of the polycarbonats is carried out in two stages. In the first stage, the reaction with phosgene is carried out at OH concentrations of between abou~ 0.01 and 0.1% by weight of OH, relative to the aqueous phase, in the presence of about 0.1 to ~.5 mol~ o~ trialkylamine, relative to aromatic dihydroxy compound employed, and at temperatures ~ ~
in excess o~ about 70C, with dwell times less than about 5 ~ ~`
minutes. In the second stage, polycondensation is effected by adjusting the OH concentration to about 0.20 to 0.50% by ~ ;
weight, relative to the aqueous phase, optionally with further addition of trialkylamine, at temperatures of in excess of about 80C and with dwell times of in excess of about 1 minute.

The process according to the invention permits the preparation of polycondensates of high technical quality, and of particularly light color, in an economical manner.

LeA 15,514 -3-:

: -:- - ~.,, , ~ - , ., - .
:::, - .. . . . . , - "

105~5~ -Detailed Description of the Invention It was found, surprisingl~, that the reaction of the phosgene with the aqueous alkali metal sal~ solution of the aromatic dihydroxy compounds at elevated temperature can be carried out without major loss of phosgene by saponification, so that about 1.05 to 1.20 mols of phosgene suffice per mol of dihydroxy compound if the reaction is carried out at OH
concentrations of between about 0.01 and 0.10% by weight in the presence of trialkylamines, using dwell times of less -than about 5 minutes. .~`-:`'" ~.' .
Any of these three measures (OH concentration, tri-alkylamine addi.tion at the beginning of the pnosgenation and limited dwell time) alone, or in combination of only two of these process parameters, does not suffice for the preparation of high molecular aromatic polycarbonates of technically high quality at the elevated reaction temperatures required when ~`
using a chlorinated aromatic hydrocarbon as the sole poly-carbonate solvent.

If one of the process parameters is not satisfied the polycarbonates produced will contain an excessive proportion of OH end groupC~ or the reaction will take place incompletely, so that substantial proportions of the aromatic dihydroxy compounds will remain unreacted in the aqueous phase, or `j only oligocarbonates will be produced because the saponification `~
l 25 reaction of phosgene is favored relative to the polycarbonate ~ ;
;l formation reaction.

., ` ~ ~ ;
The direct addition of the catalyst, trialkylamine, ;
at the beginning of the phosgenation is of particular import- ~ -`l ance in this context. The general teaching of the art is that ~ ;~
;. ~ . .
the trialkyl~mines particularly catalyze the formation of LeA 15,514 ~4~

~L05~9 ~ `
... . . .
polycarbonate from oligocarbonates containing chlorocarbonic ~
acid ester end groups, with elimination of chloride and -carbonate, and thus also ~reatly favor the saponification of phosgene, which is an analogous reaction. Thus, it was particularly surprising that in order to prepare oligocarbon-ates with chlorocarbonic acid ester end groups, which are con-verted into high molecular polycarbonates in the second state, it is absolutely essential to add trialkylamine initially.
It is believed that this ensures that the reaction of phosgene with the alkali metal salt solution of the aromatic dihydroxy compounds to give the desired oligocarbonates with chloro-carbonic acid ester end groups, occurs.
.:
However, this is only the case if an OH concentration ~;
of between about 0.01 and 0.10% by weight, based on the ~ ;
aqueous phase, is maintained, and if the dwell times are less than about 5 minutes, preferably less than about 3 minutes. -~ ~

Higher OH concentrations (pH values) lead to chain ~ -stOpping as a result of the ormation of OH end groups, while at longer dwell times dissociation reactions of the ;
already formed carbonate structures occur. It is only the conjunction of the dwell times, the presence of catalyst during phosgenation, the phosgenation at one OH concentration ~!~
and the condensation at a higher OH concentration which makes it possible to~prepare high molecular polycarbonates of technically high quality.

It is a further advantage of the process according '`
to the invention compared to the conventional process - which is carried out at room temperature using solvents which are able to dissolve polycarbonates - that substantially higher polycarbonate concentrations in the solvent phase can be ~-selected. The upper limit is a solids concentration of about LeA 15,514 -5-- ~

105~15B9 ~ :~
30% by weight.

This is a decisive economic advantage. It permits ~ ~-better utilization of the parts of the apparatus required ~
for working up the polycarbonates, such as washing installations, ~`
pre-evaporator stages and residual solvent evaporator stages, and it allows evaporation of the solvent with substantially less energy. Additional advantages are gainQd, particularly .
with regard ~o the extraction process, which is also carried out at temperatures in excess of about 80C, since in addition to requiring less wash solution, substantially shorter extraction ~;
times are needed.

Compared to the conventional procedure, in which the phosgenation takes place with cooling to remove the heat ~;
of xeaction from the reaction of the alkali metal salt lS solution of the aromatic dihyaroxy compounds with phosgene, the heat of formation of the polycarbonate is utilized, in the present process, for heating the-system to about 70-90C. ;~

In principle, the process according to the `
invention can be carried out in two-stage reactors which ensure . .
good mixing of the reaction phases by employing special devices.
In the first reactor, the alkali metal salt solution of the aromatic dihydroxy compounds, optionally together with mono-functional phenols as chain stoppers and/or polyfunctional phenols as chain-branching agents, phosgene, optionally together with the solvent, the catalyst and an additional amount of alkali metal hydroxide to maintain the requisite OH concen-tration are introduced continuously. After an average dwell time of less than about 5 minutes, the reaction mixture is transferred to the second reaction stage in which a further amount of alkali metal hydroxide solution is introduced to ~eA 15,514 -6-, ~ -.. . . .:

~051~i~9 increase the OH concentration.

For the second reaction stage, dwell times of in excess of about 1 minute, about 1-3 minutes, suffice if the reaction i5 carried out in a reaction tube according to U.S. Patent No. 3,674,740. Longer dwell times (for example in stirred kettle cascades) of approximately 20 minutes, can be maintained without disadvantages. The working up of the reaction solution issuing from the second reactor is then effected in accordance with conventional and known processes.
Evaporation in screw equipment is preferred for isolating the ~-product from the process solvent. ~-A preferred embodiment of the present invention involves the use of the reactors illustrated in the accompany-ing drawing which~

FIGURE 1 is a schematic diagram of a circulating reactor for use in the first stage of . ~ .~
the process, and ;~

FIGURE 2 is a schematic diagram of a tube reactor for use in the second stage of the process.

The circulating reactor comprises a pipe loop having a conveyor pump 1 (for example, a centrifugal pump operating at 1450 revolutions per minute), inlet pipes 3, 4 and 5 for the reactants and an overflow 2 for the reaction solution. The reactants are introduced in the direction of ;~
the flow, before the conveyor pump, in the sequence; first, the alkali m~tal salt solution of the aromatic dihydroxy compound(s) (inlet 3), thenthe phosgene/solvent mixture (inlet

4) and finally the additional alkali metal hydroxide solution LeA 15,514 -7-. ~ ~
.. ,, ~ .

~5~589 :
(inlet 5). The minimum interv~l between successive intro-ductions should he 1 second's dwell time. The volume of the reactor is conveniently 4.25 1 or 5.7 1. The temperature is measured at point 6.

The second reactor consists, in principle, of at least three mixing zones and three dwell zones. The mixing elements 7 shown in ~igure 2 are diaphragms and the dwell zones are NW25 dwell tubes 8. A piston pump (not shown) may be used as a feed device. The dwell time in thissystem is determined by the size and number of the dwell zones: a convenient total length is 24.6 m with a total volume of 12.1 1. The apparatus is described in U.S. Patent No. 3,674,740. ~ ;

Using this combination, the requisite low dwell time in the first and second stage and a very narrow dwell time distribution can be achieved. This produces polycarbo-nates with a slight molecular weight distribution.
.: ~;
The process according to the invention is suitable for the production of polycarbonates having, in principle, any desired molecular weight Mn, such as, for example, poly-carbonates with molecular weight Mn of between 5,000 and 100,000. . "

Aromatic dihydroxy compounds which can be con-verted into high molecular polycarbonates in accordance with the process described are those which form water-soluble alkali metal salts with alkali metal hydroxides such as, for example, lithium hydroxide, sodium hydroxide or potassium hydroxide.
Among these dihydroxydiarylalkanes of the general formula 1 -LeA 15,514 -8- ~ -., . , .:. . , : : . :

:LOS~L5~9 ~/~

; HO OH
R R

wherein .
X = Cl-C6-alkylene, C2-C6-alkylidene, C5-C15 - ;
cycloalkylene, C5-C15-cycloalkylidene or `

CH3 CH3 and ;~
-C- ~ -C-R = hydrogen, chlorine, bromine or Cl-C4-alkyl such as for example, bis-(4-hydroxy-phenyl)-propane-2,2 ~bisphenol A), bis-(3,5-dichloro-4-hydroxyphenyl)-propane-2,2 -~
(tetrachlorobisphenol A), bis-(3,5-dibromo-4-hydroxyphenyl)-propane-2,2 (tetrabromo-bisphenol A), bis-(3,5-dimethyl-4-hydroxy phenyl)-propane-2,2 (tetramethylbisphenol A), bis ~4-hydroxyphenyl)-cyclohexane-1,1-(bisphenol Z) and bis-(4-hydroxyphenyl)-p- `~
diisopropylbenzene (trinuclear bisphenol A) are used preferentially.

Chlorinated aromatic hydrocarbons are employed as solvents. Chlorobenzene, dichlorobenzene and trichlorobenzene, o-, m-, and p-chlorotoluene and the known positional isomers of the chloroxylenes should be mentioned. All these solvents are insoluble in water and are good solvents for polycarbonates at elevated temperatures, while at room temperature they dissolve polycarbonates only very slightly, or swell them. In LeA 15,514 -9-.... ~ : . ~: :. . : ..

~ C~51589 principle, therefore, other solvents possessing analogous solution characteristics, are also suitable. However, t~ey are not used in practice, because they are insufficiently cheap or their chemical resistance i5 low, especially at the higher temperatures which occur in the evaporation stage.
From these points of viewr chlor~benzene is the most suitable solvent.

Among the large number of polycondensation catalysts which have been described for t~e phase ~oundary process, the trialkylamines are distinguished by being particularly active. This applies preferentially to the first stage of the process described. Triethylamine, triisobutylamine and tri-n-butylamine may be mentioned as examples.

The polycarbonates produced in accordance~with the 15 process of the invention are used as moldings and films in ;
the electrical industry. Because of their excellent color quality, they find special use in the optical field and for polycarbonate sheets used as glazing materials.

Example 1 The followin~ solutions were pumped into a circulating reactor of 4.25 1 reaction volume, as shown in Figure 1:

1. 91.2 kg~hour o~ an alkali metal salt solution of b~sphenol ~, of the follow~ng compositton: 130 kg of bisphenol ~, 631 kg of water, 103.2 kg of 45% strength sodium hydroxide solution, o.as kg of sodium borohydride,2.3 kg of p-tert.-butylphenol and 0.575 kg of triethylamine.

2. 6.7 kg~hour o~ phosgene ~ith 88 kg/hr of c~lorobenzene, and LeA 15,514-Ca -10-... . ~
~, ' .. .. . . . . .. ... , , . . - ,, . . ~ ~

~(1 5~5~ :

3. Q.5 kg/hour o 45~ strength sodium hydroxide solution .

The reaction temperature is 72C; the concentration of the OH ions in the aqueous reaction phase is 0.08~. The average dwell time is 1.4 minutes.

The oligocarbonate shows the following analytical data: Relative viscosity (0.5% strength in methylene chloride) 1.069 Saponifiable chlorine ~%] (end groups) 1.4 -OH [%] (end groups) 0.42 p-tert.-butylphenol ~] (end groups) 1.52 ~urther sodium hydroxide solution is introduced ~ ' into the emulsion issuing from the circulating reactor, so as to increase the OH ion concentration to 0.30-0.35%. The further condensation of the oligocarbonate is carried out in a reaction tube, as shown in Figure 2 and described in U.S.
Patent No. 3,674,740 hereby incorporated by reference in its entirety. The average dwell time is 4 minutes; the temperature is 83C. ;
:: :
The aqueous reaction phase contains 0~32~ of OH
and 0.51% of CO3 ; bisphenol is not detectable.

The polycarbonate solution, the solids content of which is 15.1~, is washed free of electrolyte in accordance with known processes, concentrated by evaporation and dis-charged via an evaporation extruder.

The isolated polycarbonate gives the ~ollowing data: Relative viscosity (0.5% strength in methylene chloride) 1.304 Saponifiable chlorine [ppm] <2 ~
::
LeA 15,514 -11--~OSlS~9 ::

-OH [~] ~0.01 p-tert.-butylphenol [%] 1,57 Inorganic chlorine ~ppm] <2 n l9,lQ0 Mw 32,200 U ++) 0.69 Color index ~) 0.05 _____________ , +) The polycarbonate color index is an empirical relative figure. This is to be defined in the sense that 0.05 units give a visually detectable gradation for a 4 mm ` ;

thick test bar viewed in transmitted light.
) U = heterogeneity index U = Mw Example 2 ~
The following solutions are fed into the cir- ~-`
culating reactor mentioned in Example 1: ~

1. 121.7 kg/hour of an alkali metal salt ~ ~ -solution of bisphenol A having the same composition as in Example 1.

2. 8.95 kg/hour of phosgene with 62 kg/hour of chlorobenzene and 3. 0.65 kg/hour of 45~ strength sodium hydroxide solution. ~ ' The reaction temperature is 75C; the concentration of the OH ions in the aqueous reaction phase is 0.04%. The ;
average dwell time is 1.4 minutes.

The oligocarbonate is characteriæed by the following analytical data~

Relative viscosit~ (0.5% ~trength in methylene chloride ) 1.065 Saponifiable chlorine C%] ~end group~) 1.45 heA 15,514 -12~

1~51511~9 -OH [%] (end groups) 0.47 p-tert,-hutylphenol ~%~ ~end groups) 1.45 ~ :

Further sodium h~dxoxide solution is introduced ~.
into the emulsion issuing from the circulating reactor, so as to increase the OH ion concentration to 0.30~-0~35%. The further condensation of the oligocarbonate is carried out in a reaction tube as specified in Example 1. The average dwell time is 3.9 minu~es; the temperature is 85~C.

The aqueous reaction phase contains 0.35% of OH
and 0.53% of CO3 . A test for bisphenol is negative.

The solids content of the polycarbonate solution `
is 25.3%. The working up of the polycarbonate solution and isolation of the polycarbonate are carried out as described ~:
in Example 1.

The analytical data of the polycarbonate are:
Relative viscosity (0.5% strength in methylene chloride) 1.312 Saponifiable chlorine [ppm] <2 ~:`
-OH lS] . 0.017 p-tert.-butylphenol [S] 1.51 Inorganic chlorine [ppm] <2 n 18,500 M 33,700 Color index 0.1 U 0.82 ~.
Example 3 ~:~
The following solutions are pumped into a cir-culating reactor of 5.7 1 reaction volume:

LeA 15,514 -13- ;

, : . . ~ : .::

9L~5~5~9 1. ~1,2 kg/hour of an alkali metal salt solution of bisphenol A, o~ the follo~ing composition: 130 kg of bis-phenol A, 631 kg of water, 103,2 kg of 45~ s~trength sodium hydroxide solution, 0.05 kg of sodium borohydride, Q.358 kg of 1,4-bis-[~4~,4"-dihydroxy-triphenyl)-methyl]-benzene (hepta-nuclear tetraphenol), 1.970 kg of p-tert.-butylphenol and 0.575 kg of triethylamine.

2~ 6.9 kg/hour of phosgene with 64 kg/hour of chlorobenzene an~

3. 0.55 kg/hour of 45% strength sodium hydroxide solution.

The reaction temperature is 74C the concentration of the OH ions in the aqueous reaction phase is 0.04%. The average dwell time is 2.2 minutes.

To increase the OH ion concentration to 0.25-0.30%, further sodium hydroxide solution is :introduced into the emulsion before the further condensation of the oligocarbonate -in the reaction tube. The reaction temperature is 84C; the average dwell time is 4.6 minutes. ;
. ~
The aqueous reaction phase contains 0.27~ of OH
and 0.62% of CO3 . Bisphenol is not detectable.

The polycarbonate is isolated from the solution, which contains 19.7% of solids, as in Example 1.
.~' ' ~' The polycarbonate shows the following data:
Relative viscosity (0.5~ strength in methylene chloride) 1.320 Saponifiable chlorine lpPm] <2 -OH [%] 0 05 ~ ;
Inorganic chlorine lPpm] ~2 ~."
Le~ 15,514 -14-.

~5~
Example 4 The follo~ing solution~ are pumped into a cir-culating reactor of 5,7 1 reaction volume; `

1. 95.2 kg/hour of an alkali metal salt solution of bisphenol A and bisphenol Z, of the following composition:
55.8 kg of bisphenol A, 28.2 kg of bisphenol Z, 686 kg of water, 63.1 kg of 45% strength sodium hydroxide solution, 0.06 kg of sodium borohydride, 1.45 kg of p-tert.-butylphenol and 0.177 kg of triethylamine.

lQ 2. 4.75 kg/hour of phosgene with 52 kg/hour of chlorobenzene and 3. 0.4 kg/hour of 45~ strength sodium hydroxide ~ -solution.

The reaction temperature is 78C; the concentration of the OH ions in the aqueous reaction phase is 0.05%. The average dwell time is 2.4 minutes.

Be~ore further condensation of the oligocarbonate in the reaction tube, suf~icient sodi~um hydroxide solution is introduced into the emulsion that the OH ion concentration in the aqueous phase is 0.20-0.25%. Furthermore, 0.02 kg/hour of triethylamine are added. The temperature is raised to 80-85C in the post-reactor. The average dwell time is 4.9 minutes.

The aqueous reaction phase contains 0.22% of OH ~ ;
and 0.51% of CO3 ; the test for bisphenol is negative. ;;

The polycarbonate solution contains 17.5% of solids. The product is isolatea in accordance with the customary process.
LeA 15,514 -15- ~--, . . , , : . ' . . .~ . . .
.. .. . . . . ..

~L~S~S8~

The polycarbonate i~ characterized by the following analytical data:
Relative viscosity (0.5% ~trength in methylene chloride) 1.210 Saponifia~le chlorine [ppm] 13 -OH [%] 0.04 Inorganic chlorine [ppm] <2 Example 5 The following solutions are pumped into a circu-lating reactor of 4.25 1 reaction volume:

1. 132.1 kg/hour of an alkali metal salt solution of tetrabromobisphenol A, of the following composition:
108.8 kg of tetrabromobisphenol A, 629 kg of water, 41.3 kg of 4S% strength sodium hydroxide solution, 20.75 kg of 2,4,6-tri- ?
bromophenol, 0.06 kg of sodium borohydride and 3.505 kg of ~ ~-triethylamine.

2. 5.0 kg/hour of phosgene with 89 kg/hour of chlorobenzene and 3. 1.6 kg/hour of 45% strength sodium hydroxide ;
solution.

The reaction temperature is 76C; the average dwell time is 1.2 minutes; the OH ion concentration is 0.04%.

Before entering the reaction tube, 1.8 kg/hour of triethylamine, and further sodium hydroxide solution to ;/
raise the OH `ion concentration to 0.25-0.30~, are introduced `
into the emulsion. The reaction temperature is 84C; the i ~;
average dwell time is 3.4 minutes.

The aqueous reaction phase contains 0.27% of OH ~ -and 0.62% of CO3 ; the test for bisphenol is negative.

LeA 15,514 -16~

, ~. .

LS8~1 The tetrabromohisphenol polycarbonate i9 isolated from the solution, ~hich contains 20,5% of solids~ by evapora-tion.

The polycar~onate has the following analytical data;
Relative viscosity (0.5% strength in methylene chloride) 1.047 Saponifiable chlorine [ppm] 12 -OH [%] <0-005 Inorganic chlorine CpPm] <2 Comparison The following solutions are pumped into a cir-culating reactor, of 23.5 1 reaction volume, fitted with heat exchangers for removing the enthalpy of reaction:

1. 91.2 kg/hour of an alkali metal salt solution of bisphenol A, of the following compositiQn: 130.0 kg of bisphenol A, 631.0 kg of water, 103.2 kg of 45% strength -sodium hydroxide solution, 0.05 kg of sodium borohydride and ~-2.7 kg of p-tert.-butylphenoi.

2. 7.15 kg/hour of phosgene with 92 kg/hour of ;~
a solvent consisting of 60 parts by weight of methylene chloride and 40~ by weight of chlorobenzene and ;~

3. 4.3 kg/hour of 45~ strength sodium hydroxide solution.

~he reaction temperature is 24C; the pH value of the a~ueous reaction phase is 13.5 and the average dwell time is 8.4 minutes.

The emulsion issuing from the circulating reactor, and containing the oligoca.-bonate, is mixed with further LeA 15,514 -17-`: :

~LOS~5!39 sodium hydroxide solutionr to increase or maintain the pH
value of 13,5~14, and ~ith 3,0 kg/hour of a 1% strength aqueous triethylamine solution, and the mixture is pumped through a reaction tuhe, as described in U.S, Patent No.
3,674,740 to effect further condensation.

The aqueous reaction phase contains 0.28% of OH , 0.78~ of C03 and traces of bisphenol (<0.05~

The polycarbonate is isolated in accordance with -customary processes from the solution which contains 14.6% of solids.

The polycarbonate shows the following analytical data:
. .:
Relative viscosity (0.5~ strength in methylene chloride) 1.296 Saponifiable chlorine [ppm] <2 `
-OH 1~] 0.01 ;
p-tert.-butylphenol [%] <1.85 ~ ;
Inorganic chlorine ~ppm] <2 ~n 16,000 M 30,400 U 0.87 ~;
Color index 0.3 ,;~

This comparison example which typifies conventional -:.. .
polycarbonate production by the phase boundary process clearly demonstrates that the process of the present invention produces polycarbonates of comparable quality to those prepared by the conventional pracess. It is noted that the process of the present invention produces polycarbonates which have an ;
improved color index. ~ ~

LeA 15,514 -18- ~ ;

. .... . - . :: . - - .

~0515~9 Although the invention has been described in detail in the foxegoing or the purpose o~ illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those S skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

;, .

~eA 15,514 -19- ~

- . : ' . . : . . . . -- ::

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the preparation of a polycarbon-ate by the phase boundary condensation method, by phosgenation of an aqueous alkali metal salt solution of one or more aromatic dihydroxy compounds, in which process an aromatic chlorinated hydrocarbon is used as the solvent and the synthesis of the polycarbonate is carried out in two stages, in the first stage of which the reaction of the alkali metal salt solution of the aromatic dihydroxy compound(s) with phosgene is carried out at an OH concentration of between 0.01 and 0.1% by weight of OH, relative to the aqueous phase, in the presence of 0.1 to 2.5 mol% of trialkylamine, relative to aromatic dihydroxy compound(s), and at a temperature higher than about 70°C, with a dwell time of less than about 5 minutes, while in a second stage the polycondensation is effected by adjusting the OH concentration to about 0.20 to 0.50% by weight of OH, relative to the aqueous phase, at a temperature higher than about 80°C with a dwell time of more than about 1 minute.

2, The process of Claim 1 further comprising the addition of trialkylamine in said second stage.

3. A process according to Claim 1, in which chlorobenzene is used as the solvent.

4. A process according to Claim 1 in which the aromatic dihydroxy compounds are selected from dihydroxydiaryl-alkanes of the general formula in which X is Cl-C6 alkylene, C2-C6 alkylidene, C5-C15 cycloalkylene, C5-C15 cycloalkylidene or , and R is hydrogen, chlorine, bromine or Cl-C4 alkyl.

5. A process according to Claim 4, in which the aromatic dihydroxy compounds are selected from the group Consisting of bisphenol A, tetrachlorobisphenol A, tetrabromo-bisphenol A, tetramethylbisphenol A, bisphenol Z, trinuclear bisphenol A and mixtures of these dihydroxy compounds.

6. A process according to Claim 5, wherein chloro-benzene is used as the solvent, the trialkylamine is selected from the group consisting of triethylamine, triisobutylamine, tri-n-butylamine and mixtures of these catalysts and the dwell time in the first stage is less than about 3 minutes.

7. A process according to Claim 6, wherein the alkali metal salt is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide and mixtures of these hydroxides.

8. A process according to Claim 7, wherein the phosgenation is carried out in a circulating reactor comprising a pipe loop with conveyor pump and inlet pipes for the reactants and an overflow for the reaction solution and the polycondensation reaction is carried out in a tube reactor comprising an alternating sequence of at least three mixing zones and at least three dwell zones.

9. A process according to Claim 1 in which the alkali metal salt is selected from the group consisting of lithium hydroxide, sodium hydroxide, potassium hydroxide and mixtures of these hydroxides.

10. A process according to Claim 1 in which the trialkylamine is selected from the group consisting of triethylamine, triisobutylamine, tri-n-butylamine and mixtures of these catalysts.

11. A process according to Claim 1 in which the dwell time in the said first stage is less than 3 minutes.

12. A process according to Claim 1 in which 1.05 to 1.20 mols of phosgene are employed per mol of aromatic dihydroxy compound.

13. A process according to Claim 1 in which the phosgenation is carried out in a circulating reactor comprising a pipe loop with conveyor pump and inlet pipes for the reactants and an overflow for the reaction solution and the polycondensation reaction is carried out in a tube reactor comprising an alternating sequence of at least three mixing zones and at least three dweI1 zones.

14. A polycarbonate prepared by the process of

Claim 1.